This invention relates to a machine with at least two working shafts, such as rolling mills or double-screw extruder machines. With particular reference to double-screw extruder machines, these generally comprise two shafts positioned a short distance from each other and each associated with an extrusion screw, and driven by the rotation transmitted to a gear associated with each shaft. The gear is located within fixed casing through which the shaft passes, rolling bearings being provided between said shaft and the fixed casing.
The problem with such machines is to make the extrusion screws exert high pressure on the material being worked. This is done by transmitting a high torques or power to it by the rotation of gears associated with the screw shafts.
In a known type of double-screw extruder machine, the gears associated with the screw shafts cooperate with each other.
However, because of the small distance between the axes of said shafts, it is not possible to design and construct gears able to generate high torques, such, for example, the torques required by known international standards of calculation.
Methods alternative to that stated have been proposed and implemented, however if on the one hand they enable the torque transferred to the shaft of each screw to be increased, on the other hand they lead to an increase in the machine dimensions and fracture of the toothed rims of said gears, or they result in an increase in the stresses in the bearings located between each shaft and said fixed box casing of the machine. Consequently, in these methods the limits on the torque (or power) transmitted to each shaft by the gear associated with it also depend on the mechanical characteristics of the bearings located between the shaft and the machine fixed casing, these bearings beyond a certain limit not being able to resist the stresses to which they are subjected, resulting in obvious difficulties.